1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to cosmetic covers for endoskeletal prostheses.
2. Description of the Prior Art
Exoskeletal prosthetic devices were in common use as recently as thirty (30) years ago. They are made of materials such as wood, fiberglass, or other suitable materials that may be shaped to approximate the appearance of a limb. The ability to provide the general appearance of a human limb is the primary advantage of an exoskeletal device.
Exoskeletal devices also have the advantage of being relatively easy to manufacture because they are made in one piece. Thus, they are weight-bearing and do not require supplementation with additional structural elements.
However, because an exoskeletal device is made in one piece, it cannot be adjusted as the user's gait changes and as the residual limb shrinks over time.
Endoskeletal prostheses have gradually supplanted exoskeletal devices during the last thirty years for several reasons. An endoskeletal device is stronger than an exoskeletal device of the same weight, and it can be adjusted over time as a user's gait changes and as a user's residual limb changes in size. The primary drawback of an endoskeletal prosthesis is that it has a functional, utilitarian or mechanical appearance and therefore bears little resemblance to the limb it replaces. For example, an endoskeletal prosthesis that performs the function of the tibia and Peron bones of a leg is provided in the form of straight pylon that does not resemble a human leg.
Moreover, endoskeletal prostheses are not one-piece structures. For a below knee amputee, an endoskeletal device will include a form-fitting socket for receiving a residual limb, a pylon that performs the function of the tibia and Peron bones in a human leg, a prosthestic foot that takes the reaction force from the ground and transmits it to the pylon and socket and ultimately to the bone structure of the amputee, and connection hardware that interconnects the various components. More particularly, connection hardware is required between the distal end of the socket and the proximal end of the pylon and between the distal end of the pylon and the proximal end of the prosthetic foot.
An above knee prosthesis requires all of the below-knee components, and a prosthetic knee joint as well. It provides angular motion similar to that of a human knee.
One advantage of having separate components is that a worn part may be replaced without replacing the entire prosthesis. An exoskeletal prosthesis, on the other hand, must be replaced in toto if any part thereof requires replacement.
Because endoskeletal prostheses are machine components with inadequate aesthetic value, the art has developed several techniques for covering the pylon with a cosmetic covering that approaches the appearance of a human limb. A common cosmetic covering is a foam known in the art as prosthetic foam. It can be shaped to substantially conform to the shape of a limb. Typically, the sound limb of an amputee is used as a model. The foam that covers the pylon is sculpted to look like the sound limb in shape and size. It is then spray painted with a flexible paint having a skin tone that matches the coloration of the sound leg. A skin tone stocking is then placed over the painted foam and a cosmetic cover is placed over the stocking. Depending upon the color of the cosmetic cover, it may or may not be painted. Thus, the cosmetic cover ensleeves the prosthetic foot, the foam-covered pylon, the prosthetic knee, and at least the distal end of the socket in above-knee amputation applications. In below knee applications where no prosthetic knee is required, the cosmetic cover ensleeves the prosthetic foot, the foam-covered pylon, and at least the distal end of the socket.
Two types of cosmetic covers have been developed for use with endoskeletal prostheses. Each of them has advantageous as well as disadvantageous properties.
The first type of cosmetic cover is substantially inelastic. Cosmetic covers exhibiting low elasticity are mass produced in many different sizes and shapes in the hope that a reasonable match may be found for each user. However, due to the wide variation in such parameters as ankle and calf geometry, both in circumference and longitudinal profile, a suitable match is seldom made between such an “off the shelf” product and the geometry of an amputee's limb. Moreover, due to the low elasticity of such a cover, it cannot conform to the surface details in the prosthetic foam that covers the pylon of an endoprosthetic device. A prosthetist may work diligently and with artistry to fashion a prosthetic foam cover that provides a good match to the amputee's sound limb, only to have the details of the prosthetic foam obliterated by an inelastic cosmetic cover that inadequately conforms to the realistic surfaces created by the prosthestist.
The second type of cosmetic cover has good elasticity characteristics and thus does not hide the work of the prosthetist. This type of cosmetic cover is desirable because it conforms exactly to the surface contour of the underlying prosthetic foam. Accordingly, the appearance of the prosthesis closely matches the appearance of the sound limb.
Highly elastic form-fitting cosmetic covers are thus initially more desirable than the inelastic type. Unfortunately, the bias provided by the elasticity continuously bears against the underlying prosthetic foam, applying a uniform pressure to it. After a few weeks or months, depending upon such factors as the stiffness of the foam and the elasticity of the cosmetic cover, the underlying foam sustains a set and shrinks. A uniform shrinkage in circumference is of little or no concern throughout most sections of the prosthesis, but in an above-knee prosthesis, it is problematic at the junction between the distal end of the prosthestic knee joint and the proximal end of the prosthetic foam, and the junction between the proximal end of the prosthetic foot and the distal end of the prosthetic foam. Neither the prosthetic knee joint nor the prosthetic foot are foam-covered so such parts do not undergo shrinkage. Thus, in above knee applications, a visible line of demarcation forms at the juncture between the prosthetic knee joint and the proximal end of the foam, and between the distal end of the foam and the prosthetic foot. In below knee applications, a visible line of demarcation forms at the juncture between the proximal end of the foam and the distal end of the socket and the distal end of the foam and the proximal end of the prosthetic foot. These lines of demarcation destroy the semblance of normalcy created by the careful sculpting and painting of the foam and the contour-following elasticity of the cosmetic cover.
Both types of cosmetic covers are thus understood to have significant drawbacks. What is needed is a cosmetic cover that provides the form-fitting benefits of a highly elastic cover without also causing the shrinkage of the underlying foam. The needed cosmetic cover would conform exactly to the underlying foam, as would a highly elastic cover, but would not apply a pressure thereto.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how these inherently contradictory requirements could be fulfilled.